1. Cross Reference to Related Application
Reference is directed to commonly assigned U.S. patent application Ser. No. 07/958021, now pending, filed on even date herewith in the names of Richard L. Timp, Michael W. Schultz, and John H. Morehead, and entitled ADJUSTABLE LENGTH PUNCH SET ASSEMBLY.
2. Technical Field
This invention relates generally to punch guide assemblies such as those usable with multiple-station turret punch machines, and more particularly to stripper plate assemblies.
3. Description of the Prior Art
Multiple-station turret punch machines such as Amada Lyla series Model 50-50-72 can provide up to 72 different punch stations for use in conjunction with a like number of opposing dies. In such a machine, each punch station operates as a punch set holder for a removable punch set that includes a centrally disposed punch surrounded by a punch guide and biased by a punch spring. Even with the flexibility afforded by a 72-station machine, the operator may wish to change some or all of the punch set and die combinations from time to time. For instance, the operator may wish to utilize a different punch blade shape or size in a punch set. It is desirable to minimize the time required and make it simple to so change the punch and die components, and thereby reduce down time for the punch machine.
In the punching operation, after the punch blade enters the workpiece surface, the edge of the cut surface will tend to follow the punch blade as it retracts. As a result, "stripping" occurs; that is, the edges around the punched hole will bear outwardly and necessitate further time consuming finishing operations.
To prevent stripping, the punch guide may be provided with a stripper plate. The stripper plate has an opening such that a punch blade will fit snugly therethrough but, yet will be able to axially move freely through the opening. In use, the punch guide is oriented with the stripper plate flush against the workpiece surface. Then, when the punch blade retracts from the workpiece, the edges of the workpiece around the punch hole will be prevented by the stripper plate from following the retracting punch blade.
One such punch guide stripper plate configuration incorporates the stripper plate as an integral part of the punch guide itself. Since the size and shape of the stripper plate hole must coincide closely with the punch blade, however, each such punch guide may only be used with one matching punch. Consequently, interchanging punch and die combinations may be inconvenient, since the operator must change not only the die and punch, but the punch guide as well.
Another configuration uses flattened metal clip or the like to retain a removable stripper plate at the end of a punch guide. This allows the use of a number of different punch blades with each guide, since only the stripper plate need be changed for each new punch blade. These spring clip structures, however, have not provided completely satisfactory performance. Often, the workpiece surface will have a thin coating of oil or other fluid. When the stripper plate meets the workpiece surface, a suction may be created. When this occurs, the stripper plate may be pulled out of place and damage may result to the workpiece and to the stripper plate. Down time may also become a problem. Finally, these clips also tend to weaken with usage, aggravating the above-noted problems.
Another configuration is shown in commonly assigned U.S. Pat. No. 4,092,888 which depicts a punch guide assembly using a resilient, flat retaining ring to hold a removable stripper plate in place.
And in yet another configuration, commonly assigned U.S. Pat. No. 4,248,111 depicts a punch guide assembly that makes use of stripper plate holding tabs that are formed on clips attached parallel to the primary axis of the punch guide.
A further locking ring stripper plate assembly is disclosed in commonly assigned U.S. Pat. No. 4,446,767 wherein a locking ring 13 is fitted in matching circumferential grooves in a stripper plate 12 in the punch guide sleeve 11. The free ends 31 of the locking ring 13 include tabs 32 that may be spread apart and locked into position by the locking ring expansion lock 14. Thus, although installation and removal of the stripper plate is relatively simple, it involves handling the loose ring 13 and the cap screw used as the locking ring expansion lock 14. The manipulation of these small, difficult-to-handle parts, may be time consuming.
Other mechanisms for retaining stripper plates in the ends of punch guides are described in U.K. patent specification 1 251 843 and U.S. Pat. Nos. 3,079,824 to Schott, 3,540,339 to Killaly, 4,947,718 to Whistler, and 4,989,484 to Johnson, et al.
In the U.K. patent specification, an O-ring 25 in annular mating grooves in the punch guide sleeve and the stripper plate provides a snap fit of the stripper plate 21 to the punch guide 18. The '824 patent also illustrates a snap ring 38 for retaining stripper plate 36 in position. Such snap rings may not be strong and reliable enough to lock stripper plates in position.
The '339 patent employs retainers 60 and spring-mounted elements 56 for engagement against v-shaped annular detent grooves 57 in the edge of the stripper plate 62. Attachment and removal involves loosening the retainers 60 and moving them aside to snap in or unsnap the spring-loaded catches 56 in or out of the grooves. The redundant attachment mechanism requires additional steps in releasing or locking the stripper plate.
The '718 patent shows in FIGS. 5, 7 and 14 the use of spring clips 194 attached to the punch guide and engaging internally-threaded annual flanges 196 in the stripper plate 46 in a fashion similar to the '111 patent. Such spring clips may not be strong enough for large diameter punch sets and may weaken with repeated use.
The '484 patent discloses a complex locking ring 80 with positioning springs 90 and 92 located within a groove and positioned between a pair of diametrically opposed pins 94, 96 that engage other pins, such as 98, to hold the ring 80 in the lock position. The stripper plate 74 is held in place in the locking ring by centrally extending flanges 109 and pin receiving slots 110 to cover the pins 74D. To remove or replace the stripper plate 74, the locking ring 80 is turned about the axis of the punch assembly against the compression of the springs 90, 92, thereby aligning the pin receiving slots 110 with the pin 74D and allowing the stripper plate 74 to be removed and re-inserted in the fashion of a bayonet-lock mechanism. Then by pushing the stripper plate in and depressing release pin 112, the springs 90, 92 rotate locking ring 80 on the box 76 so the flanges 109 cover the pins 74D thereby holding the stripper plate 74 securely in place on the end of the punch assembly 10. This rotatable retaining ring and stripper plate assembly constitutes a number of small parts, such as pins and springs, that add to complexity and fabrication costs. Moreover, the stripper plate retaining ring itself is removed when the stripper plate is released which can lead to its loss or damage if dropped.
Despite the effort put into designing various types of attachment mechanisms for stripper plates, a need remains for simple, strong, reliable and inexpensive to manufacture stripper plate locking mechanisms that are easy and quick to use in releasing or attaching the stripper plate, do not include small loose parts and securely hold the stripper plate when locked.